1. Field of the Invention
The present invention relates to a clamping cylinder actuator attached to a fixed member of a machine, such as a base to hold a workpiece fixedly on the fixed member for machining by a machine tool or the like and, more particularly, to a clamping cylinder actuator having a front end cover having a back joining surface to be joined to a fixed member of a machine, such as a base.
2. Description of the Related Art
A first related art clamping cylinder actuator disclosed in JP-B No. Sho 62-5739 (Publication 1) has a cylinder, and a front end cover having a back joining surface and a boss fitted in the bore of the cylinder with an O ring held between the cylinder and the boss of the front end cover. A second related art clamping cylinder actuator disclosed in JP-A No. 10-315083 (Publication 2) has a cylinder, a front end cover formed integrally with the cylinder, and the front end cover has a back joining surface to be joined to a fixed member of a machine, such as a base.
In the first related art clamping cylinder actuator disclosed in Publication 1, the boss of the front end cover needs a longitudinal dimension sufficient to form an annular groove to hold the O ring therein in the boss. Therefore, the length of the cylinder must include a length corresponding to a length in which the boss must be formed to form the annular groove for the O ring therein in addition to a length corresponding to the effective stroke of a piston that moves axially in the cylinder bore and hence the cylinder is inevitably long. The clamping cylinder actuator needs many bolts for fastening the front end cover and a back end cover to the cylinder, which requires troublesome part management and increases assembling work.
Although the second related art clamping cylinder actuator disclosed in Publication 2 does not have such problems, the cylinder and the front end cover cannot be formed of different materials, respectively because the cylinder and the front end cover are formed in an integral unit by forming.
Both the first and the second related art clamping cylinder actuator have the back joining surfaces to be joined to a fixed member of a machine. Since the front end cover is fastened to the fixed member with bolts with the joining surfaces thereof in direct contact with the fixed member, it is possible that the bolts are loosened by vibrations generated by the machine.
In the second related art clamping cylinder actuator disclosed in Publication 2, side ports for a working fluid are formed in a side surface of the front end cover and end ports are formed in the joining surface of the front end cover, and a pipe is connected to either the side ports formed in the side surface or the end ports formed in the joining surface. When the side ports are used and the end ports are not used, O rings are placed between the joining surface and the fixed member so as to surround the end ports to create nonleaking union between the front end cover and the fixed member. Handling the small O rings is troublesome and O rings are often lost.
A known clamping cylinder actuator has a cylinder provided on its outer surface with a position sensor for measuring the position of a piston fitted in the cylinder. Since the position sensor juts out from the outer surface of the cylinder, the clamping cylinder actuator needs a large space for installation, the cylinder needs a long machining time and hence the cylinder is costly.
A front end cover integrally provided with a guide member cannot be used as a part of another clamping cylinder actuator that does not need any guide member.
It is possible that a cutting fluid or a cutting oil leaks into the position sensor and cause the position sensor to malfunction. Therefore, although the position sensor is leak-proofed, it is undesirable, in respect of durability, to use the clamping cylinder actuator in an environment where the position sensor is exposed to the cutting fluid.
Accordingly, it is an object of the present invention to provide a clamping cylinder actuator having a front end cover having a back joining surface to be joined to a fixed member, in which a seal structure is held between the front end cover and a cylindrical member to which the front end cover is joined, and the seal structure prevents the loosening of bolts fastening the front end cover to the fixed member, under vibrations. It is also an object of the present invention to provide a clamping cylinder actuator with side ports and end-ports formed in the front end cover, in which an O ring is not necessary to be used for sealing the end ports.
Another object of the present invention is to reduce the manufacturing cost of a clamping cylinder actuator provided on the outer surface of the cylinder thereof with a magnetic sensor and to improve the appearance of the same.
For a further object, the present invention provides a clamping cylinder actuator requiring a small number of fastening parts necessary for fastening together its components including a front end cover, a cylinder and a back end cover, easy to assembly and satisfactory in appearance. The present invention also provides a clamping cylinder actuator having a front end cover provided with a small number of through holes. Further, the present invention provides a clamping cylinder actuator including a front end cover, a back end cover and a cylinder which can be fastened together in an airtight fashion with bolts. Furthermore, the present invention provides a clamping cylinder actuator having a front end cover available to clamping cylinder actuators of other types and effective in reducing the number of parts, and capable of being manufactured at a low manufacturing cost.
For a still further object, the present invention provides a clamping cylinder actuator having a position sensor for measuring the position of a piston in a cylinder, and a sensor cover capable of satisfactorily covering the position sensor so that the position sensor may not be wetted with a cutting fluid or the like.
According to a first aspect of the present invention, a clamping cylinder actuator attached to a fixed member to clamp down a workpiece on the fixed member comprises: a cylindrical member; a front end cover provided with an opening and joined to the front end of the cylindrical member; a piston rod axially slidably extended through the opening of the front end cover; a back end cover disposed at the back end of the cylindrical member; and a gasket held between the cylindrical member and the front end cover to make a sealed joint between the front end of the cylindrical member and the front end cover; wherein the front end cover is attached to the fixed member with a joining surface of the back surface thereof extending outward from a sealing surface of the back surface thereof corresponding to the front end of the cylindrical member in contact with the fixed member, and the gasket covers the sealing surface and the joining surface of the back surface of the front end cover. The joining surface of the front end cover can be partly or entirely covered with the gasket.
Preferably, the cylindrical member includes a cylinder, a back end of which is joined to the back end cover, and the gasket makes a sealed joint between the front end of the cylinder and the back surface of the front end cover. When the cylindrical member includes a cylinder, and a guide member holding member disposed between the cylinder and the front end cover to hold a guide member engaged in a helical guide groove formed in the piston rod, the gasket makes a sealed joint between the front end surface of the guide member holding member and the back surface of the front end cover.
Since the gasket making a sealed joint between the front end cover and the cylindrical member extends over the joining surface, bolts fastening the front end cover to the fixed member will not be loosened by vibrations generated by a machining operation because the gasket is elastic. Since the front end cover and the cylindrical member (or the cylinder) are separate members, the cylindrical member and the front end cover can be formed of different materials, respectively, which facilitates reducing the cost. Since any O ring is not necessary to make a sealed joint between the front end cover and the cylindrical member, the front end cover may be provided with a short boss that is fitted in the cylinder bore of the cylindrical member, so that the cylindrical member can be formed in a small length.
Preferably, a side port connected to the cylinder bore of the cylindrical member is formed in a side surface of the front end cover, an end port connected to the side port is formed in the joining surface of the front end cover, and a portion of the gasket covering the joining surface serves as a sealing member for sealing the end port. When the end port is not used, the gasket makes a sealed joint between the front end cover and the fixed member. When a pipe is connected to the end port, the gasket makes a sealed joint between the pipe and the end port. Since any small sealing member, such as an O ring, is not used for sealing the end port, troubles attributable to the loss of a sealing member and work for attaching the small sealing member can be avoided.
Preferably, the clamping cylinder actuator further comprises a gasket held between the back end of the cylinder and the back end cover to make a sealed joint between the cylinder and the back end cover. The length of a boss of the back end cover to be fitted in the cylinder bore may be smaller than a length in which the boss must be formed when a sealed joint is made between the back end cover and the cylindrical member by an O ring, which is effective in forming the clamping cylinder actuator in a small length.
The present invention is applicable to a clamping cylinder actuator of a unilateral piping type comprising a cylindrical member, a piston rod, a piston connected to the piston rod and fitted in the cylinder bore of the cylindrical member, and a front end cover joined to the front end of the cylindrical member and provided with a pair of side ports respectively communicating with front and back pressure chambers on the front and the back side of the piston. A pair of end ports are formed in a joining surface of the front end cover so as to communicate with the pair of side ports, respectively, and a portion of the gasket covering the joining surface serves as a sealing member for sealing the pair of end ports.
The present invention is featured by matters set forth in claims 8 to 20.
Since the front end cover and the cylindrical member (cylinder, etc.) are separate members, the cylindrical member and the front end cover can be formed of different materials, respectively, which facilitates reducing the cost of the clamping cylinder actuator. Since any O ring is not necessary to make a sealed joint between the front end cover and the member to which the front end cover is joined, the front end cover may be provided with a short boss that is fitted in the cylinder bore of the cylindrical member. Since the gasket held between the front end cover and the member to which the front end cover is joined extends over both the sealing surface and the joining surface of the back surface of the front end cover, bolts fastening the front end cover to the fixed member will not be loosened by vibrations generated by a machining operation because the gasket is elastic.
Since the gasket is held between the joining surface and the fixed member, the cutting fluid wetting the front end cover is unable to flow over the outer surface of the cylinder. Since the portion of the gasket extending over the joining surface serves also as a sealing member for sealing the end ports, a sealed joint is made between the end ports and the fixed member when the end ports are not used. When pipes are connected to the end ports, the gasket makes a sealed joint between the pipes and the end ports. Since any small sealing member, such as an O ring, is not used for sealing the end ports, troubles attributable to the loss of a sealing member and work for attaching the small sealing member can be avoided.
Since the gasket is held between the back end of the cylinder and the back end cover, to which the back end of the cylinder is joined, to make a sealed joint between the cylindrical member and the back end cover, the length of the boss of the back end cover to be fitted in the cylinder bore may be small and which enables forming the clamping cylinder actuator in a small length.
The cylinder may be formed from a generally cylindrical aluminum shape provided with a bore. The cylinder can be formed simply by cutting the aluminum shape in a desired length. The aluminum shape may be originally provided with an axial hole for unilateral piping and sensor holding grooves for holding sensors therein, which makes it possible to omit additional boring work. The sensors held in the sensor holding groove do not project outward from the outer circumference of the cylinder, the clamping cylinder actuator can be installed in a narrow space. The back end cover may be formed by processing an aluminum shape provided with grooves corresponding to the sensor holding grooves of the cylinder and holes for bolts. Therefore, the back end cover does not need any machining work for forming those grooves and holes and can be fabricated at a low cost. The aluminum shape for forming the cylinder may be formed by drawing. The cylinder bore can be formed by drawing with a high accuracy and does not need any machining, which reduces the cost of the clamping cylinder actuator. The front end cover may be formed of a ferrous material and magnets may be attached to the piston so as to be axially spaced a long distance apart from the front end cover. Magnetic fields created by the magnets are not affected by the front end cover and the sensor functions with reliability.
The front and the back end cover may be fastened to the front and the back end, respectively, of the cylinder with common bolts, and the bolts may be extended through longitudinal through holes formed in the cylinder. The bolts are concealed and the clamping cylinder actuator has an improved appearance. When the clamping cylinder actuator is used in a vertical position with the front end cover facing up, chips produced by machining a workpiece and fallen on the front end cover do not fill up threaded holes and chips can be smoothly removed.
The guide member holding member may be separate from the front end cover covering the front end of the cylinder, the guide member holding member may be provided with a guide member for guiding a rotary motion, and the front end cover may be used also as a front end cover that does not need any guide member. When rotary clamping cylinder actuators and axial clamping cylinder actuators are produced simultaneously, front end covers of the same type can be used for fabricating clamping cylinder actuators of different types, which is very advantageous from the viewpoint of part management and clamping cylinder actuators of different types can be manufactured at low manufacturing costs. Since the back end cover, the cylinder, the guide member holding member and the front end cover are fastened together with the same bolts, those components can be fastened together with a small number of bolts and the clamping cylinder actuator can be assembled by small man-hours.
The front end cover may be formed so as to be used in combination with the cylinders of clamping cylinder actuators of different types, and may be provided with ports in both its side surface and its back surface. Therefore, either the ports formed in the side surface or those formed in the back surface can be used for desired one of two piping systems, and the front end cover can be employed in clamping cylinder actuators of different piping systems, which reduces the kinds of parts. The front end cover may be used in combination with a cylinder provided with ports in its front portion. A piping system in the back end cover can be enabled by closing the ports formed in the side surface and the end surface of the front end cover, and different piping systems can be employed in clamping cylinder actuators of different operation types.
The cylinder of the clamping cylinder actuator may be covered with a sensor cover to water-proof the cylinder perfectly. Malfunctioning of the sensors embedded in the outer surface of the cylinder due to wetting with the cutting fluid can be surely prevented when the clamping cylinder actuator is used in an environment in which the cylinder is wetted continuously with the cutting fluid. A portion of the sensor cover corresponding to the outer circumference of the cylinder may be formed of a transparent material to enable the visual observation and checking of the operation of the sensors.
In a clamping cylinder actuator of a linkage type, the front end cover and a support pin can be formed of materials meeting functions required of the front end cover and the support pin, the front end cover can be used in combination with cylinders of different types, the support pin can be simply and firmly attached to the front end cover, and the clamping cylinder actuator can be formed in small dimensions at a low manufacturing cost.